如何在 Java 中打印出字符串中的特定字母
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How to print out specific letters within a String in Java
提问by ProgrammingBeginner
I have been set a task to print out the 2nd, 3rd and 4th letter of a name within a String variable.
我已经设置了一个任务来打印出字符串变量中名称的第 2、3 和 4 个字母。
So for example the name is John and I want to print out the letters 'o, h and n only'
例如，名字是约翰，我只想打印出字母“o、h 和 n”
I was wondering if there is a specific method which I can use to carry out this task, if not what is the best approach to take?
我想知道是否有一种特定的方法可以用来执行这项任务，如果没有，最好的方法是什么？
采纳答案by robotlos
EDITas @KevinO pointed out, determining whether the name length or 4 is smaller solves issues that would cause exceptions. I updated to incorporate this input.
Depends on how you're trying to print it. You can use a forloop and iterate starting at the 1st index of your String namelike so:
正如@KevinO 指出的那样编辑，确定名称长度或 4 是否更小可以解决会导致异常的问题。我更新以合并此输入。
取决于您尝试打印它的方式。您可以使用for循环并从您String name喜欢的第一个索引开始迭代：
String name = "John";
for(int i = 1; i < Math.min(name.length(), 4); i++){
System.out.print(name.charAt(i));
}
Sample Run:
示例运行：
run:
ohn
BUILD SUCCESSFUL (total time: 0 seconds)
运行：
ohn
BUILD SUCCESSFUL（总时间：0 秒）
You could print out theCharacterone at a time like:
您可以一次打印出Character一个，例如：
System.out.print(name.charAt(1)); //print character at index 1
System.out.print(name.charAt(2)); //print character at index 2
System.out.print(name.charAt(3)); //print character at index 3
This might be unsafe because you're not sure if the name will in be in fact at least 4 Characterslong.
Sample run:
这可能不安全，因为您不确定名称实际上是否至少为 4Characters长。示例运行：
run:
ohn
BUILD SUCCESSFUL (total time: 0 seconds)
运行：
ohn
BUILD SUCCESSFUL（总时间：0 秒）
Or perhaps the easiest way which is also safe, you could print it out using String.substring()which takes in a range, like so:
或者也许是最简单的方法也是安全的，您可以使用String.substring()它在一个范围内打印出来，如下所示：
System.out.println(name.substring(1, Math.min(name.length(), 4)));
This results in:
这导致：
run:
ohn
BUILD SUCCESSFUL (total time: 0 seconds)
运行：
ohn
BUILD SUCCESSFUL（总时间：0 秒）
回答by Sajeev
You can do that by using charAt function on String . The following version of code should do what you are asking for.
您可以通过在 String 上使用 charAt 函数来做到这一点。以下版本的代码应该可以满足您的要求。
public static void main(String[] args) {
String input = "John";
if (input != null && input.length() > 1) {
System.out.println(input.substring(1, Math.min(input.length(), 4)));
}
}
回答by Aaron
Assuming the name always has at least 4 letters in it, this code will work:
假设名称中始终至少包含 4 个字母，则此代码将起作用：
public static void main(String[] args) {
String name = "JOHN";
System.out.println(name.substring(1,4));
}
